Penetration of Boron from Topically Applied Borate Solutions

Borate penetration relies on diffusion when borate and glycol-borate preservatives are applied to the surface of wood. This study evaluated the extent of borate penetration in framing lumber as a function of preservative formulation, wood moisture content, and diffusion time after treatment. In Phase I of the study, end-matched specimens were conditioned to target average moisture contents of 15, 25, or 35 percent, briefly immersed in borate formulations, and then placed into wooden frames to minimize air exchange during diffusion. Penetration in these specimens was generally less than 5 mm (or 35% of the cross section) regardless of treatment solution, target moisture content at time of treatment, or diffusion period (2, 4, or 8 wk). Assay of boron concentrations after 8 weeks of diffusion also indicated that the boron was concentrated in the outer 5 mm of the wood. Diffusion appeared to have been limited by the relatively rapid drying of the specimens, even with the restricted air movement within the wo...